1993 Buick Roadmaster Heater core

How do you replace the heater core in a 1993 Buick Roadmaster Wagon-loaded. I have found no good results on "AllData" or "Mitchell". It looks like the the way across twhole main instrument panel must be removed. Also have the "Haynes" book (no comment). Also no help from 2 Buick Dealers. The cover panels are removed, the glove box is moulded on to the inner panel, the inner support panel which goes all the way accross the car. All lower supports that are accessible are removed. That "main" panel is attached with bolts to the fire wall how many and where is unknown. Cannot see them from the front with the heater/ac push button controls. So far no one has been able to come up with any drawings or explaination as to how to do this. Have new core. Any assistance in resolving this situation would be greatly appreciated.